XenApp 7.13 - Director - Data source unresponsive or reported an error. View Director server event logs for further information.

After upgrading my XenApp from 7.12 to 7.13 - I got an error message on the Director:

Data source unresponsive or reported an error. View Director server event logs for further information.

Event Viewer logs on DDC were showing:

The data source 'Unknown error.' ('http://DDC1.domain.local/Citrix/Monitor/OData/v3') responded with an unexpected error.

User: 'domain\username'
Console operation: 'Retrieving connection failures by type details…'

Additional information:
' (0)'

The database dont have a space in the name and the two DDC have their own FQDN in the

Service.AutoDiscoveryAddresses.

The fix is to do the following:

• Login to your Citrix DB
• Navigate to your Monitoring DB
• Right click and run a new query

SELECT *

  FROM [ENTER-DB-NAME].[MonitorData].[Machine]

  where [DesktopGroupId] = '00000000-0000-0000-0000-000000000000'

• The above command will return the "NULL" entry in the DB. If you have it, that's your problem.
• To delete this NULL entry, you have two options:
• OPTION 1: Go to Monitoring DB > Tables > monitordata.desktopgroup > edit top 200 rows > delete the NULL entry
• OPTION 2: You can run this, in case you have a reference conflict while tryign to delete the NULL Entry in option 1. New Query on Monitoring DB and run the following:

declare @did uniqueidentifier

set @did = '00000000-0000-0000-0000-000000000000'

delete from MonitorData.Session

where machineid in (Select Id from MonitorData.Machine

where DesktopGroupID = @did)

delete from MonitorData.Machine

where DesktopGroupId = @did 

delete from MonitorData.DesktopGroup

where id = @did